1. Related Application
The present application is related to an application filed simultaneously herewith, owned by the same Assignee, entitled “Method and Device to Generate a Measurement Sequence For Operating a Magnetic Resonance System That is Adapted to the Time Raster of the System,” having U.S. Ser. No. 12/540,475.
2. Field of the Invention
The present invention is in the field of programming of measurement sequences for magnetic resonance. In particular, the invention proposes a formal description of a measurement sequence using a magnetic resonance sequence model, whereby the programming of measurement sequences for magnetic resonance can be largely automated.
3. Description of the Prior Art
Magnetic resonance (MR) scanners (also called nuclear magnetic resonance tomographs) today are a basic component of the clinical routine for examination of patients in hospitals. Moreover, magnetic resonance scanners can also be used for the examination of animals and/or biological samples.
Measurement sequences are necessary to control the MR scanner.
The generation of MR images in an MR scanner requires an exact, temporal workflow between the radio-frequency excitation of the spins, the spatial coding and the detection of the resonant response of the spin. The temporal workflow of the excitation, preparation and detection is called a pulse sequence or measurement sequence. A single segment of the measurement sequence can be classified according to its purpose. This division is designated as a time slice. A time slice is thus an established time segment within the measurement sequence that serves a specific purpose, for example the excitation of the nuclear spins. Time slices contain control instructions for the MR scanner. The time slices precisely establish what the MR scanner has to do and at which point in time. A series of time slices can be executed in the MR scanner because it contains all instructions and their temporal correlation to the control of the MR scanner. Alternatively, the execution of the time slices with a control unit connected with the MR scanner is also possible.
A measurement sequence can be executed as a series of time slices in the MR scanner. Within the measurement sequence for execution in an MR scanner, the time slices are joined seamlessly (i.e. without gaps). Each of the time slices has a specific length, and at least one pulse with a pulse shape is associated with every time slice. Each of the time slices can be associated with a type from the set: transmission type for transmission of RF power; reception type to detect the resonant response of the nuclear spins; and warp type to prepare the nuclear spins. Time slices of the transmission type are used as excitation pulses to excite the nuclear spins, to refocus the nuclear spins, and in a hybrid form that serves both for excitation and for refocusing. In addition to these, there are time slices in which RF energy is emitted and/or an RF signal is received. Moreover, RF pulses are known for the inversion of the nuclear magnetization, called inversion pulses.
Over the years many MR sequences or measurement sequences have been developed for different purposes. For example, it is possible to significantly affect the contrast of an image by the selection of a measurement sequence. The preparation of the spin system—for example by means of pulses for RF excitation, gradient pulses, wait times and so forth—has a decisive influence on the quality and property of the acquired MR image.
A measurement sequence for execution in an MR scanner in a clinical everyday situation typically is composed of 106 different time slices that are involved in a sensitive temporal correlation among one another. The creation of the measurement sequences has developed into its own field of MR physics.
Conventionally, measurement sequences for execution in an MR scanner have been prepared by a sequence programmer. This occurs in one of the known programming languages, normally C++, which describes all properties and the temporal sequence of the time slices. This means that the measurement sequence has conventionally been generated manually in order to exist in a completely parameterized form and with permissible parameter values for execution in the MR scanner.
The administration (management) of so many parameters is laborious and prone to error. Errors of the programmer in the sequence programming can lead, for example, to the situation that an MR examination of a patient is terminated by the MR scanner and/or a supervision module because, for example, necessary parameters are not populated with a value. Extensive (for example temporal) connections exist between individual parameters so that an MR image can be acquired. If these connections are not maintained, the desired MR image is not acquired. The checking of these extensive connections by the sequence programmer is very time-consuming and error-prone.
When a new measurement sequence for execution in an MR scanner is developed, the discovery of a permissible parameter set that generates the desired MR image is additionally a laborious process. The user of the MR scanner and/or the programmer must change individual parameters in many iteration steps until the parameter set contains permissible values that are matched to one another as a while so that the measurement sequence is executable in the MR scanner.
A need therefore exists to describe measurement sequences as concisely and comprehensively as possible. A measurement sequence description is thus sought. At the same time, such a concise description may not limit the freedom of the programmer to create new measurement sequences.
Moreover, a need exists for a method that automatically develops a measurement sequence in a form such that the measurement sequence is executable in the MR scanner. For current MR scanners, this can mean to automatically translate the measurement sequence specification into a series of time slices that can be executed in the MR scanner.